Telecommunications equipment, computers and other electrical apparatus comprise arrays of interconnected circuit boards. Each circuit board comprises a rigid planar substrate with a plurality of integrated circuit chips and/or other electronic memory means disposed thereon. This active circuitry on some of the circuit boards is electrically connected to conductive regions along one edge of the planar substrate to enable engagement of these circuit boards with a socket mounted on another circuit board. In this context, the circuit board on which the socket is mounted typically is called the mother board. The board engaged in the socket may be called a daughter board, an edge card, a SIP (single in-line package), a circuit module, a memory module add-on or a SIMM (single in-line memory module). For consistency, the board engageable in the socket will be referred to herein as a SIMM, while the corresponding socket will be referred to as a SIMM socket. This terminology is intended to encompass all such edge connectors and the boards engageable therewith.
The prior art SIMM socket houses a plurality of electrically conductive terminals. Each terminal includes a board mounting portion which is soldered or otherwise connected to circuitry on the board and a mating portion for electrically contacting a specific conductive edge region on the SIMM. A SIMM often is removed and replaced to alter the functions that can be performed by the electrical apparatus in which the SIMM is disposed. Additionally, a SIMM may be removed if any of the many circuits thereon fail or to facilitate trouble-shooting elsewhere in the electrical apparatus.
Prior art SIMM sockets merely relied upon generally linear pushing and pulling of the SIMM into or out of the socket. More particularly, the movement of the edge of the SIMM into the socket would cause contact beams of the terminals in the socket to resiliently deflect and subsequently exert contact forces against the conductive regions along the edge of the SIMM. Although the wiping action achieved during insertion of the SIMM into the prior art socket may be desirable, the insertion forces can damage the fragile terminals. As a result, SIMM sockets and other edge connectors have evolved to eliminate or reduce insertion forces.
Extremely desirable and effective SIMM sockets enable the SIMM to be inserted at a first angle with minimal insertion forces, and subsequently permit the SIMM to be rotated into a second angle for achieving high quality electrical connection with the resilient contact beams of the terminals. These more recent prior art SIMM sockets include latch means for lockingly but releasably retaining the SIMM in an alignment corresponding to a high quality electrical connection with the terminals in the socket. Desirable SIMM sockets of this general type are shown in U.S. Pat. No. 4,575,172 which issued to Walse et al. on Mar. 11, 1986 and U.S. Pat. No. 4,713,013 which issued to Regnier et al. on Dec. 15, 1987. The two above identified patents are assigned to the assignee of the subject invention, and the disclosures thereof are incorporated herein by reference.
It will be noted that in each of the patents identified above, the SIMM socket is defined by a plastic housing having terminals mounted therein. The housing is unitarily molded with plastic mounting pegs which are receivable in mounting apertures of the circuit board for lockingly retaining the SIMM socket thereto. The typical pegs are disposed to define pairs of deflectable legs that initially deflect upon insertion through a hole in the circuit board, and which then resiliently return to an undeflected condition for retaining the socket on the board.
It will also be noted that the SIMM sockets shown in the above identified patents are unitarily molded to include deflectable plastic latches having ramped forward faces that are engaged by the SIMM as the SIMM is rotated into its fully seated alignment. The ramping forces developed between the SIMM and the forward face of each latch urges the latches away from one another and permits continued rotation of the SIMM. Upon full seating of the SIMM, the plastic latches resiliently return to an undeflected alignment for retaining the SIMM in the socket. The plastic latches of the prior art SIMM socket are intended to be manually rotated away from one another to enable removal of the SIMM.
The above described SIMM sockets have received exceptional commercial success in view of the proliferation of computers, advanced telecommunication equipment and other electrical apparatus requiring memory circuitry. However, it has been found that as SIMM sockets have experienced wider use, they have been used by people who are less familiar with the intended operation of the socket. In particular, technicians, computer users and the like were found to grossly overdeflect the SIMM socket latches to effect removal of the SIMM, thereby snapping the latches off at their base. In response to this problem virtually all SIMM socket manufacturers incorporated separate overstress prevention walls to limit the distance by which the SIMM socket latches can be rotated away from one another. Overstress prevention walls are shown, for example, in U.S. Pat. No. 4,832,617 which issued to Brown on May 23, 1989, U.S. Pat. No. 4,850,891 which issued to Walkup et al. on July 25, 1989 and U.S. Pat. No. 4,826,446 which issued to Juntwait on May 2, 1989.
The combination of deflectable plastic latches and overstress walls on SIMM sockets has not eliminated problems associated with the use of SIMM sockets. In particular, users are known to attempt removal of a SIMM by merely rotating the SIMM against the latches thereby exerting forces on both the SIMM and the latches that neither structure was intended to encounter. These rotational forces can damage the circuitry on the SIMM and can snap the latches. Other users attempt to manually rotate the latches in directions other than away from one another. These manual forces on the latches generally will not damage the SIMM but may break the latches. Still other users employ screwdrivers to apply even higher levels of improper force. Attempts to design plastic SIMM latches that avoid breakage have resulted in either latches that are too difficult to deflect, latches that do not adequately retain the SIMM in the socket or latches that may fail after too few cycles of insertion and removal.
In addition to the problems associated with latch breakage, SIMM sockets have experienced breakage of the plastic mounting means for securing the socket to the circuit board. In particular, the mounting pegs must be sufficiently flexible to easily deflect during mounting onto a circuit board, while also being sufficiently strong to retain the SIMM socket in position. Any movement of the SIMM socket relative to the circuit board can cause failure of the soldered electrical connections between the terminals in the socket and the conductive regions on the circuit board. The plastic mounting pegs have been known to break during shipping or initial installation attempts. As a result, the sockets are either rejected or are mounted with a broken mounting peg that can not adequately hold the socket to the board.
A SIMM may assume any of several different thicknesses and may be made from materials having different strength characteristics. These variations in SIMM characteristics may require different latch specifications for the SIMM socket. In particular, the relative distance between the rear wall of the SIMM socket and the locking face of the latch must vary in accordance with the thickness of the SIMM. Additionally, the flexibility of the latch may have to vary in accordance with the relative strength characteristics of the SIMM. All plastic SIMM sockets can be retooled to achieve these various design requirements. However, retooling of this type is expensive and time consuming.
The above identified copending application Ser. No. 553,016 overcomes most of the deficiencies of the prior art. However, it is desirable to provide still further improvements. For example, it is considered desirable to more positively control the deflection of the latches such that the latches deflect about parallel axes which extend substantially orthogonal to the SIMM receiving slot in the socket. Positive prevention of deflection of the latches about axes extending parallel to the SIMM receiving slot should be avoided. Similarly, twisting of each latch also should be prevented. In other embodiments it may be desirable to provide greater retention of the latch on the SIMM socket, while in still other environments it may be desirable to further reinforce the overstress wall of the SIMM socket. Additionally, it may be desirable to provide a latch with a SIMM engaging face that is less likely to be damaged by improperly exerted forces thereon.
In view of the above, it is an object of the subject invention to provide a SIMM socket having a latch means that substantially prevents breakage.
A further object of the subject invention is to provide SIMM socket latches that are easily deflectable, that provide positive locking and that avoid breakage.
It is an additional object of the subject invention to provide SIMM socket latch means that can accommodate boards of different dimensions and strength characteristics without complete retooling of the socket.
Another object of the subject invention is to provide a SIMM socket having latch means that positively resists damage from improperly applied forces thereon.
A further object of the subject invention is to provide a SIMM socket latch that readily permits variations to the moment arm thereof.
Yet another object of the subject invention is to provide a SIMM socket latch that resists twisting along its length without substantially increasing forces required to achieve deflection.
Still a further object of the subject invention is to provide a SIMM socket latch that is positively limited to deflection about a single axis.
A further object of the subject invention is to provide a SIMM socket with a reinforced overstress prevention wall.